Fig. 2. (a) The fluorescence responses of N-CBT (5 μM) toward different concentrations of ONOO⁻ from 0 to 50 μM, the solvent is a mixture of ethanol and PBS (5 : 5, v/v, pH 7.4); (b) and (c) fluorescence response of N-CBT (5 μM) toward ROSs, RNSs, bio-thiols and metal ions (the final concentration: GSH and H₂O₂ were 1 mM, Cys, Hcy and metal ions were 500 μM, the others were 50 μM), 1: blank; 2: Cys (500 μM); 3: Hcy (500 μM); 4: GSH (1 mM); 5: ONOO⁻ (50 μM); 6: H₂O₂ (1 mM); 7: TBHP (50 μM); 8: ClO⁻ (50 μM); 9: ¹O₂ (50 μM); 10: OH˙ (50 μM); 11: NO (50 μM); 12: HNO (50 μM); 13: Ca²⁺(500 μM); 14: Fe²⁺(500 μM); 15: Fe³⁺ (500 μM); 16: K⁺ (500 μM); 17: Mg²⁺ (500 μM); 18: Na⁺ (500 μM), the solvent is a mixture of ethanol and PBS (5 : 5, v/v, pH 7.4); (d) the effect of pH on the fluorescence intensity of N-CBT (5 μM) and N-CBT (5 μM) with ONOO⁻ (50 μM), the solvent is a mixture of ethanol and PBS (5 : 5, v/v, pH = 6, 7, 8, 9, 10). All data represent the fluorescence intensity at 518 nm, λ_ex = 405 nm, slit widths are set at 5.0 nm, cuvette width is 1 cm.